Formation of metastable phase during crystallization of lithium magnesium pyrophosphate glass

In the Li ₂O-MgO-ZnO-P ₂O ₅ system, glasses based on the LiMgP ₂O ₇ composition were synthesized using the melt-quenching method, specifically focusing on two series: Li _4xMg _2(1-x)P ₂O ₇ and Li ₂Zn _yMg _(1-y)P ₂O ₇. Li ₂MgP ₂O ₇ (33.3mol% Li ₂O, 33.3mol% MgO, 33.3mol% P ₂O ₅ ) showed an X-ray diffraction pattern similar to Li ₂ZnP ₂O ₇ (LZPO) when heat-treated near its crystallization onset temperature, as determined by differential thermal analysis (DTA). However, at 700 °C, thermal decomposition into multiple phases, including Li ₄P ₂O ₇, was observed. In the Li _4xMg _2(1-x)P ₂O ₇ glass series, LZPO-type crystals formed in the range of x = 0.5 to 0.75. The quasi-binary system of Li ₂MgP ₂O ₇ and Li ₂ZnP ₂O ₇, represented by Li ₂Zn _yMg _(1-y)P ₂O ₇, formed glasses across all compositions. These glasses formed LZPO-type crystals showing lithium-ion conductivity at the crystallization onset temperature. A surface crystallization tendency was confirmed where crystals grew from the surface towards the interior of the glass substrate.